Spencer Dickerson of the U.S. Contract Tower Association, an airport industry group, said contract towers are taking a disproportionate brunt of the closures.
Medicare is a government-run program, and services are bought on a contract basis by the Centers for Medicare and Medicaid Services and the American Associationof Retired Persons.
The "cover to contract" campaign, by members of the National Union of Teachers and the National Associationof Schoolmasters Union of Women Teachers, is in protest at what the unions call a crisis in teacher recruitment.
The early movers included Dave Bates, the president of the Allied Pilots Association who spearheaded the merger effort but stepped down in August after pilots rejected a contract deal he had backed.